Homework two-2016. Please turn in questions 8 and 9 on W.
1.A classic example of natural selection:
Please read the paper on industrial melanism.
a. State Kettlewell’s primary hypothesis.
b. List the different ways Kettlewell tested his hypothesis.
c. Mark-recapture, first used to test the effectiveness of natural selection, is now of the most common “experimental” methods used in ecological research. It is important that you understand this method.
Try this problem.
Calculate the relative fitnesses for typical and melanistic moths in Dorset, England if the number of moths released was 406 melanistic and 393 typical. They recaptured 19 of the melanistic moth marked and 54 of the typical.
c. Determine which type of evidence, frequency distributions (correlations), mark-recapture work, experiments on predation or modeling, best supports Kettlewell’s hypothesis. Justify your answer.
2. A bit on correlation
To examine adaptation from an evolutionary focus requires a good understanding of trend analysis and the comparative method. We will do more on the comparative method under the topic of phylogeny. Many studies in evolutionary medicine will relay on correlations rather than experimentation.
The experiment has long been accepted as a way to gather evidence for or against hypothesis. Yet often it is impossible to conduct the appropriate experiments to examine major evolutionary questions. Making more observations has always been a legitimate way of testing scientific hypotheses.
Example: Every time the sun sets in the west and rises in the east I am more convinced that it will continue to do so. (reason for the sun rising----http://www.universetoday.com/18117/why-does-the-sun-rise-in-the-east-and-set-in-the-west/)
Correlations are trends, collections of observations, measured by the tightness of fit between two variables. Statistics is often used to determine how closely data points fit to a straight line drawn between them (linear regression).
Three relationships with the same slope, but different amounts of “scatter” around an imagined best fit line.
Lately non-experimental science has been dubbed discovery science. This seems a humble name for methods that have given use major theories in biology such as "the cell theory" and "the grand synthesis or evolutionary theory".
3. Dr. Snow used observations and correlations to determine the cause of cholera.
An observation based on interviews and city medical records.
"The most terrible outbreak of cholera which ever occurred in this kingdom, is probably that which took place in Broad Street, Golden Square, and the adjoining streets, a few weeks ago. Within two hundred and fifty yards of the spot where Cambridge Street joins Broad Street, there were upwards of five hundred fatal attacks of cholera in ten days. The mortality in this limited area probably equals any that was ever caused in this country, even by the plague: and it was much more sudden, as the greater number of cases terminated in a few hours.
The mortality would undoubtedly have been much greater had it not been for the flight of the population. Persons in furnished lodgings left first, then other lodgers went away, leaving their furniture to be sent for when they could meet with a place to put it in."
A correlative map put together by Snow.
a. How do you think Snow used observation and mapping to pinpoint the source of cholera.
b. Read the following passage from Snow's work. Why did Snow feel it important to investigate individuals in the area of the outbreak that did not get cholera?
“There are certain circumstances bearing on the subject of this outbreak of cholera which require to be mentioned. The Workhouse in Poland Street is more than three-fourths surrounded by houses in which deaths from cholera occurred, yet out of five hundred and thirty-five inmates only five died of cholera. . . . The workhouse has a pump-well on the premises, in addition to the supply from the Grand Junction Water Works, and the inmates never sent to Broad Street for water. If the mortality in the workhouse had been equal to that in the streets immediately surrounding it on three sides, upwards of one hundred persons would have died. “
“ There is a Brewery in Broad Street, near to the pump, and on perceiving that no brewer's men were registered as having died of cholera, I called on Mr. Huggins, the proprietor. He informed me that there were above seventy workmen employed in the brewery, and that none of them had suffered from cholera--at least in a severe form--only two having been indisposed, and that not seriously, at the time the disease prevailed. “
“ The men are allowed a certain quantity of malt liquor, and Mr. Huggins believes they do not drink water at all; and he is quite certain that the work-men never obtained water from the pump in the street. There is a deep well in the brewery, in addition to the New River water. “
4. Testing yourself on correlation:
a. Can you describe the correlation implied by this graph.
b. What can you learn from looking at outlying points.
.
5. More recent examples of natural selection in action:
Examine the examples on this web site. Briefly explain why the examples are good examples of natural selection directing the changes observed.
http://evolution.berkeley.edu/evolibrary/article/microexamples_01
Genetic drift
6. Examine the examples on these two websites.
http://evolution.berkeley.edu/evolibrary/article/samplingerror_01 and
http://evolution.berkeley.edu/evolibrary/article/bottlenecks_01
What are the differences between founder effects and bottlenecks?
7. A simulation on genetic drift.
Please visit these web pages and answer the following questions.
http://pages.ucsd.edu/~dkjordan/resources/clarifications/MitochondrialEve.html
and
http://www.cals.ncsu.edu/gn/ex/mit-eve.html
a. Who is mitochondrial eve?
b. Run the simulation 5 times until only one Eve remains. What is the smallest number of generations it took to fix mitochondrial type? What was the longest number of generations it took to fix mitochondrial type?
8. Examples of genetic drift
http://evolution.berkeley.edu/evolibrary/news/101201_panthers
a. What is the problem facing Florida panthers?
http://evolution.berkeley.edu/evolibrary/news/080901_dftd
b. What is the role of genetic drift in creating the problem facing Tasmanian devils.
http://evolution.berkeley.edu/evolibrary/news/070701_cheetah
c. How is sexual selection helping to combat the problems in variation caused by a bottleneck.
Selection of drift:
9. How do you judge?
For larger populations look for evidence of correlation between environmental change and phenotypic change. If not there, look for conditions favorable for potent genetic drift, such as small population sizes, etc.
Determine whether natural selection or genetic drift is driving evolution in each of the following cases. Defend your answer.
a. Case one: humans. A storm blows a small ship of Swedish sailors, most blonde with blue eyes, on to an island. The same storm has claimed most of the native males of reproductive age, most with dark hair and brown eyes, who drowned when their fishing boat capsized. Many of the Swedish sailors stay on the island and marry native girls. Two hundred years later, about 30 % of the island children have blue eyes.
b. Case two: sticklebacks. Fish were trapped in coastal lakes formed some 10,000 years ago by a retreating glacier. The lakes are isolated from one another. Indeed, two of the lakes are located on separate islands along the coast. Yet each of the three lakes wound up with the same to non-interbreeding varieties of stickleback, the bulky benthic type and the actively swimming limnetic type. Isolation is due to mate preference. Benthics mate with benthics, both from their own lake and others, while shunning all limnetics.
c. Case three: fruit flies. Samples were taken from Europe and North American populations of flies. Both show an increase in wing size from south to north. But the European populations lengthened the part of the wing closest to the body, while those in North America extended the outer segment.
d. Case four: bacteria. Over 11 years researchers raised 24,000 generations of E.coli. All 12 of Lenski's cultures experience the same stresses, a daily boom and bust cycle, in which the bacteria are transferred to fresh glucose medium every 24 hours, than undergo 6 hours or so of plenty followed by 18 hours of starvation. All 12 lines have adapted to this regime; they grow about 60% faster than the original lines and are about 2x the size of the original lines. At the genomic level however, the similarities differ. The sequence changes found in different lines were different and had accumulated at different rates leading to conspicuous and significant discrepancies between genomic evolution and its visible effects.
10. For smaller amounts of time, try to monitor gene frequency.
a and b are graphs that simulate genetic drift under the gene frequencies and numbers indicated. Can you explain the difference between graphs? Hint: Compare the number of time the alleles are fixed.
In c, only the numbers in the population have changed, can you explain the difference in the graphs.
d. What would the graph look like if only selection was driving evolution?
e. What would the graph look like if selection and drift were driving evolution?